379 volt gauge wiring schematic

http://www.supermiller.com/pdf/sk25762.pdf
This is from an online schematic, if no one else can help we have the service manual at the shop, I wont be back there til friday to see if diagram is different than this one.

 

Ground
+ positive
guage illumination terminal

 

I was going to say the same though I believe where that blue plug is in the back is would be the spot that a socket and bulb would go with 2 leads off it.

I could be wrong though because someone told I was once before but I brushed it off because I believe I am always right.

 

It is hard to read. I will check the master book tomorrow but heres a couple of thoughts for tonight, can you remove the gauge from the housing to see what the terminals connect to on the rear of the gauge? If so and the odd ball terminal goes to nothing then maybe its a universal housing and pete gauge just uses the +/- terminals?
In looking at my 389 gauges today, most of them have a red idiot light built into each face of the gauge. Therefore, id have an illumination circuit, a ground and a hot, and another feed wire from the ecm(?) or sensor to light up the warning lamp part of the gauge. Do you think your odd terminal is just that- a lead from the ecm or else not, im not sure. We have a 2000 379 I might pop the panel off tomorrow and see how many wires the voltmeter has to it.
I wonder if different 379 interior packages/options have different gauge faces that
would use the same housing but feature the idiot light within the gauge thing?

 

I just pulled the panel off our 379, theres nothing connected to the 3rd terminal on the voltmeter- its the same gauge as your picture in post